WASHINGTON — An armed man who jumped the White House fence this month made it far deeper into the mansion than previously disclosed, overpowering a Secret Service agent inside the North Portico entrance and running through the ceremonial East Room before he was tackled, according to a member of Congress familiar with the details of the incident.

The man, Omar J. Gonzalez, who had a knife, was stopped as he tried to enter the Green Room, a parlor used for receptions and teas, said the congressman, Representative Jason Chaffetz of Utah, the Republican chairman of a subcommittee looking into the security breach. Earlier, Secret Service officials indicated that Mr. Gonzalez, 42, had only made it steps inside the North Portico after running through the door.

The new development, first reported by The Washington Post, raised immediate questions about whether the Secret Service had been forthright in its initial accounts of the episode. It will set the stage for an explosive congressional hearing on Tuesday when lawmakers say they intend to grill Julia Pierson, the director of the Secret Service, about whether an undisciplined culture inside the long-heralded agency has eroded its ability to protect the president and his family.

The hearing is set to focus on a series of security embarrassments over the last several years, including a breach that occurred when a couple crashed a state dinner in 2009, a 2011 incident when bullets struck the White House, scandals involving drinking and prostitution on overseas trips in 2012 and 2013, and 16 separate cases of people scaling the White House fence in the last five years. Ms. Pierson became director in 2013.

According to a law enforcement official briefed on the current investigation, uniformed Secret Service officers at the White House failed to follow several of the agency’s protocols. Although the protocols call for an officer to be standing outside the North Portico door, there was no officer there as Mr. Gonzalez made his way up the steps. The officer who was stationed inside the door failed to lock it after an alarm was sounded that someone had jumped over the fence, the official said.

“At all times there is supposed to be someone at the outside and the inside of the door,” the official said. “The intruder was running so fast that he gets right past the woman who didn’t lock the door. She tries to catch him, and eventually she and another officer tackle the man to the ground, but by that time he was pretty far in.”

It has been unheard of in recent decades for an intruder to force his way into the White House, even if only a few steps inside what is supposed to be one of the most secure buildings in the world. Officials in Washington were stunned that Mr. Gonzalez was able to pass by the staircase that leads to the White House family quarters and get as far as the East Room, the ballroom where the cellist Pablo Casals played for President John F. Kennedy and where President Obama announced the death of Osama bin Laden.

Mr. Chaffetz said that Mr. Gonzalez ran from the north front of the White House into the Entrance Hall and then into the 80-foot-long East Room, where he was finally stopped by Secret Service officers at a Green Room entrance near the south side of the mansion. The Obama family was not home at the time.

In addition, Mr. Chaffetz said a system designed to alert agents that a breach of security was in progress apparently did not work as intended, allowing Mr. Gonzalez to surprise the officer at the door. Mr. Chaffetz said that he was told the “crash box” had been silenced or muted at the request of White House ushers, who had complained the boxes were too noisy.

“It’s an astounding set of facts,” said Representative Gerald E. Connolly of Virginia, a Democratic member of the committee. “It just boggles the imagination and is deeply destabilizing in terms of public confidence in the Secret Service and how it is carrying out its mission.”

The new details are strikingly different from what Secret Service officials first said happened on Sept. 19, the day Mr. Gonzalez breached the building. In a statement on Sept. 20, the agency said Mr. Gonzalez “was physically apprehended after entering the White House North Portico doors” — leaving the impression that Secret Service officers tackled Mr. Gonzalez just steps after he opened the door and walked through. Secret Service officials said nothing in their public comments to suggest otherwise.

In its initial briefings, the Secret Service did not inform the Department of Homeland Security, which oversees the agency, that the intruder had made it so far inside the White House, according to an official familiar with the conversations. But the official said that until a final investigation was complete, the department could not confirm or deny the new account.

White House officials also did nothing in the last week to correct the impression that Mr. Gonzalez had been stopped just inside the front door of the building. Josh Earnest, the White House press secretary, was asked repeatedly about the incident in the days after it happened and did not disclose the extent of the breach.

Asked about the new disclosures on Monday, Mr. Earnest referred to comments he made to reporters earlier in the day. Mr. Earnest said that the president retained “full confidence” in Ms. Pierson but that the incident was “an issue that the president is obviously concerned about.”

It is unclear when Mr. Obama learned of how far Mr. Gonzalez had penetrated the White House. West Wing officials previously said Ms. Pierson briefed Mr. Obama about the incident during an Oval Office meeting last week, but they would not say what details she disclosed at the time.

On Tuesday, Ms. Pierson will appear before the House Committee on Oversight and Government Reform, and will hear from lawmakers in both parties who said they would demand explanations for other breaches as well, including recent revelations about a slow and incomplete response by the Secret Service to the incident in 2011, when a man fired seven shots into the south side of the White House.

“Have there been some other serious breaches?” Mr. Chaffetz said. “Absolutely.” He said the 2011 incident was “about as bungled as could possibly be,” but he said lawmakers on the committee have received numerous reports about security breaches that have not yet been made public.

The Washington Post reported that Mr. Obama and Michelle Obama were furious that they had not been made aware of the 2011 incident until days after it happened.

Representative Elijah E. Cummings of Maryland, the senior Democrat on the committee, said he would insist that Ms. Pierson explain why Secret Service officials in charge of protection around the grounds of 1600 Pennsylvania Avenue appear not to have listened to agents on the ground that night in 2011 who believed shots had been fired at the White House. “I want to know what culture allows that to happen in an organization that is supposed to be the most elite protective agency in the world,” Mr. Cummings said.

Matt Apuzzo and Charlie Savage contributed reporting.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Armed Intruder at White House Got to East Room. Order Reprints | Today’s Paper | Subscribe